Automotive applications typically using an air pump, specifically a turbine, supercharger, or exhaust driven turbocharger, include gasoline, natural gas or diesel internal combustion engines. Other automotive applications also include fuel cells and fuel reformers, both requiring large volumes of air and often supplied by a turbine pump. While a bypass valve may be utilized for any pump configuration, the exhaust driven turbocharger is the typical application. The exhaust driven turbocharger is a free-spinning turbine with a shaft-separated split impeller, one end receiving force and a rotational moment from the exiting exhaust gases, the other end applying a pumping effect. As it is a free-spinning turbine, if the load on the air side suddenly increases due to a sudden decrease of demand by the engine, such as during deceleration, the pump will see a dramatic decrease in rotation and the corresponding sudden decrease in cooling effect, lubricating effect, as well as a high fatigue load on the impeller blades.
For the purpose of reducing the load on the turbocharger during sudden decreases of downstream flow, a bypass valve is typically applied to allow the impeller to continue moving air from the low pressure side to the high pressure side at a rate now set by the impeller speed. It is desirable to have a valve which can respond quickly when deceleration, load change or load shift point occurs, and recover quickly as when acceleration or higher load is suddenly required. When not energized, it is desirable to minimize bypass leak and corresponding decrease in pump efficiency when full throughput is required from pump. This must be satisfied with robustness as well as cost efficiency, while at the same time not introducing undesirable noise, vibration and harshness, or noise, vibration, harshness (NVH). In a cost efficient configuration, the handling characteristics must not be sacrificed and it is desirable to have a feature that retains all the stationary and moving components as an assembly, without adding to the overall size of the device, nor adding cost. Retention prevents the moving parts from separating from the device during assembly, shipping and handling, and the subsequent possible damage and loss of critical functional parts.
Thus, there is a need to provide an improved air bypass valve that includes retention structure for retaining moving parts prior to installation of the valve.